The present invention relates to a wound covering agent, a wound covering material and a wound treatment method. More specifically, it relates to a wound covering agent and wound covering material which are effective for cleaning wound sites and removing necrotic tissue and which have excellent hydrophilicity and biocompatibility, and to a wound treatment method employing the wound covering material. According to the present invention, it is possible to alleviate pain by wiping or covering wounds, ulcer or burn injury sites with the wound covering material, and to treat sites of skin loss due to wounds or burn injury by accelerating re-epithelialization and granulation. It is also effective for improving the quality of life (QOL) after healing by preventing secondary infection and preventing scar and contracture formation caused by prolonged inflammation.
Management methods for wounds and diseases such as traumatic wounds, dermatomic wounds and the like are largely classified as either dry dressing in which the wounded site is left open or is protected with gauze to positively maintain a dry condition, or wet dressing, which involves covering it with a urethane film or the like with low moisture permeability.
The former method is aimed at positively promoting crust formation to reduce external bacterial infection and prevent loss of body moisture; however, it is known that drying of the wound surface delays re-epithelialization and that adhered crust peels off when the covering material is exchanged, thus injuring the wound surface and prolonging the healing time.
The latter method occludes the wound site to prevent infection before it can occur and to hasten wound healing by providing an appropriate moist environment. With exudative wounds, however, accumulating wound fluid can be reabsorbed on the wound surface causing reinfection, and therefore a hydrophilic fibrous material is used in combination to control excess exudate.
Ointment therapy with antibiotics is also employed with lint cloths or gauze against the risk of infection with wide-area burn injury or third degree burns. However, neo-granulated tissue penetrates the fiber structure as it develops, and this is associated with problems in that delayed wound healing occurs accompanied with injury of granulation when the wound covering is exchanged. Japanese Patent Laid-open Publications No. SHO 51-56040 and No. SHO 63-51865 disclose non-sticky wound covering materials, but they do not always provide fully satisfactory results.
According to Japanese Patent Public Inspection No. HEI 7-504459, there is disclosed a wound covering material which is one of working examples of a polymer composition comprising a polymer having a zwitterionic pendant group with another polymer having desirable mechanical and/or physical properties; however, no specific polymer composition components or wound coverings are provided.
It is an object of the present invention to provide a wound covering material that has high biocompatibility, is safe and has low skin irritation, and that accomplishes proper healing of wounds without adhesion of crustation or granulation to the wound covering material, as well as a wound covering agent that can be used to produce such a wound covering material.
It is another object of the present invention to provide a wound treatment method that accomplishes proper healing of wounds in a safe manner without irritation to the skin.
As a result of searching for wound covering materials with excellent biocompatibility in order to solve the aforementioned problems, the present inventors found out that a specific polymer with a group related to the polar group of a phospholipid (phosphatidylcholine), which is a major component of biological membranes, is stable, and has a moisture retaining effect and a function that accelerates wound healing, to complete the present invention.
That is, the present invention provides a wound covering agent comprising a polymer having a group represented by the following formula (I): 
where R1, R2 and R3 are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and m represents an integer of 2-4.
The present invention further provides the aforementioned wound covering agent wherein the polymer is selected from the group consisting of a homopolymer of monomer (a) having a group represented by formula (I) above, a copolymer of monomer (a) having a group represented by formula (I) above and another monomer (b), a crosslinked polymer thereof, and mixtures thereof.
The present invention still further provides the aforementioned wound covering agent wherein the monomer (a) is a monomer represented by the following formula (II): 
where R1, R2, R3 and m are the same as in formula (I), R4 represents a hydrogen atom, methyl group or xe2x80x94CH2xe2x80x94COOH, R5 represents an alkylene group having 2 to 10 carbon atoms and n represents an integer of 0-10.
The present invention still further provides the aforementioned wound covering agent wherein the monomer (a) is 2-methacryloyloxyethyl phosphorylcholine represented by the following formula (III): 
The present invention still further provides the aforementioned wound covering agent wherein the polymer is selected from the group consisting of a copolymer of the aforementioned monomer (a) and monomer (b), a crosslinked polymer thereof and mixtures thereof, and the monomer (b) is selected from the group consisting of monofunctional monomers, crosslinkable monomers and mixtures thereof.
The invention still further provides the aforementioned wound covering agent wherein the polymer comprises a unit represented by the following formula (IV): 
where R1, R2, R3 and m are the same as in formula (I), R4 represents a hydrogen atom, methyl group or xe2x80x94CH2xe2x80x94COOH, R5 represents an alkylene group having 2 to 10 carbon atoms and n represents an integer of 0-10.
The present invention still further provides the aforementioned wound covering agent wherein the polymer also comprises a unit represented by the following formula (V): 
where R6 represents a hydrogen atom, methyl group or xe2x80x94CH2xe2x80x94COOH, R7 represents a hydrogen atom, a carboxyl group or an alkoxycarbonyl group having 2 to 6 carbon atoms and X represents the group xe2x80x94Yxe2x80x94Z1, a crosslink represented by xe2x80x94Yxe2x80x94Z2xe2x80x94Yxe2x80x94 or a crosslink represented by 
where Y represents xe2x80x94COOxe2x80x94, xe2x80x94CONHxe2x80x94, -oC6H4xe2x80x94, -mC6H4xe2x80x94, -pC6H4xe2x80x94, xe2x80x94OCOxe2x80x94 or a dimethoxysilyl group; Z1 represents a hydrogen atom, a sodium atom, a cyano group, a vinyl group, a glycidyl group, an alkyl group having 1 to 4 carbon atoms, a hydroxyalkyl group having 2 to 4 carbon atoms, a dihydroxyalkyl group having 2 to 4 carbon atoms, a pyrrolidonyl group, a sulfonic acid group, a sodium sulfonate group, 2-ethylhexyl group, trimethoxysilylpropyl group, triethoxysilylpropyl group, methyldimethoxysilylpropyl group, an oxyalkyl group having 2 to 6 carbon atoms or a 2-20mer group that is made of oxyalkylene groups each having 2 to 6 carbon atoms and that has a hydrogen atom or methyl group at terminal thereof; Z2 represents xe2x80x94(AO)rxe2x80x94Axe2x80x94 where A is an alkylene group having 1 to 12 carbon atoms and r is an integer of 0-20; and Z3 represents a trivalent or tetravalent hydrocarbon group having 3 to 12 carbon atoms, and wherein the proportion of units represented by formula (V) of the total of the number of units represented by formula (IV) and the number of units represented by formula (V) in the polymer is in a range of larger than 0% and no greater than 99%, and the number average molecular weight thereof is 5,000-1,000,000.
The present invention still further provides a wound covering material comprising the wound covering agent.
The present invention still further provides a wound treatment method that comprises a step of covering the wound site of a subject with the wound covering material to protect the wound site.